﻿10 BULLETIN 1H6, U. S. DEPARTMENT OF AGRICULTURE. 



This means that the copper sprays may in some way accelerate the 

 transformation of sugar to starch during the active stages of growth. 

 The Green Mountain tubers did not show this tendency. The ratio 

 <>f sugars to starch decreased greatly during growth, the percentage 

 of sugars decreasing while the percentage of starch increased. The 

 ratio of sucrose to dextrose increased during the growth of the tubers, 

 the dextrose practically disappearing at maturity. At the time the 

 first and second analyses were made the three early varieties of 

 potatoes contained a higher percentage of dextrose plus sucrose than 

 the late variety (Green Mountain). This higher sugar content may 

 be characteristic of early varieties and may be associated with the 

 rapid growth which these varieties make. The unsprayed tubers, 

 with the exception of the Green Mountain, usually showed a higher 

 ratio of sugar to starch than the tubers from the copper-sprayed 

 plants. 



It is evident that marked changes take place in the potato during 

 development. Apparently these changes are influenced in some way 

 by the copper sprays, higher percentages of solids, starch, and 

 nitrogen usually following the application of copper sprays to 

 potato vines. 



These data may be of value in determining when a potato is 

 mature. It appears that the sugar to starch ratio, as suggested by 

 Appleman (&), as well as the ratio of protein to amid nitrogen and 

 the percentage of total nitrogen as amid nitrogen, is of value. The 

 percentage of starch in terms of total solids may be used. Appar- 

 ently certain changes in the ash constituents may be applied to solve 

 the question. 



EFFECT OF COPPER SPRAYS ON YIELD AND COMPOSITION OF TUBERS. 



1917 AND 1918 DATA (MAINE). 



In 1916 and again in 1917 potato plants which received copper 

 sprays gave higher yields than those which received no copper spray. 

 It was therefore thought that the copper sprays might influence the 

 composition of the tubers as well as the yield. Late blight was 

 severe in 1917 in this locality but was slight in 1916 and 1918. Dur- 

 ing the season of 1917 Green Mountain potatoes were sprayed at 

 Presque Isle, Me., using 5-5-50 Bordeaux, Pickering sprays contain- 

 ing various amounts of copper, and a barium- water-copper-sulphate 

 spray containing 0.7 per cent of copper sulphate. Duplicate deter- 

 minations for solids were made on four samples of tubers from (a) 

 5-5-50 Bordeaux-sprayed vines (1.25 per cent copper sulphate) ; 

 (h) Pickering-sprayed vines (0.64 per cent copper sulphate) ; and 

 (c) unsprayed vines grown in the same field. All of the vines were 

 sprayed seven times during the season, lead arsenate being used on 

 all of the plants. 



The four samples of tubers from the Bordeaux-sprayed vines 

 averaged 21.45 per cent solids; those from the Pickering-sprayed 

 vines, 21.49 per cent solids; and those from the check vines, 20.65 

 per cent solids. Similar results were obtained with this variety of 

 potatoes in Maine during the season of 1918. 



